1. Field of the Invention
The present invention relates to method of climbing up/down a step by a bogie provided with a plurality of wheels under the main body of the bogie, as well as to the bogie and a wheelchair provided with the bogie.
2. Description of the Related Art
A conventional bogie is provided with a plurality of wheels mounted under a main body thereof, a motor for traveling that drives the wheels and a control unit for controlling an output of the motor and a steering direction of the wheels.
Such bogie automatically travels on the ground under control by the control unit. Also, the bogie can climb up or down a step lower than a radius of the wheel, because of friction between the step and the wheel that has contacted with the step.
However, a conventional bogie has a problem that it cannot climb a step that is higher than a radius of the wheel.
Also, when a conventional bogie is climbing up/down a step, such situation often takes place that the wheel is not contacting with a wall face of the step, or other wheels than those in contact with the step lose contact with the ground and float in the air. In such a case a grip force necessary for traveling becomes unavailable. Also a greater impact is imposed on the main body of the bogie while climbing up/down the step or when the climbing action has been completed. Further, since the wheels cannot support the bogie, the bogie is prone to lose its balance.
Meanwhile, for controlling a motion of a robot arm (manipulator), an impedance control is performed wherein a position and force are simultaneously controlled by adjusting inertia, viscosity and rigidity of an object of control.
When a displacement vector x follows the following formula in relation to a driving force F, a coefficient matrix {M, D, K} is defined as impedance characteristics.Mx″+D(x′−xd′)+K(x−xd)=F
M stands for mass characteristic, D for damping characteristic, and K for rigidity characteristic.
Also, xd is a target position of the object of control. In case where xd is constant, the displacement vector x follows the following formula against the driving force under a condition of Δx=(x−xd):Mx″+Dx′+KΔx=F
By adopting a complex argument s as a differential operator and utilizing a Laplace transform of Δx and F (ΔxL and FL), this formula can also be expressed as:(s2M+sD+K)ΔxL=FL
Based on this, a formula of transfer function G(s) that represents input/output characteristics of the input F and output Δx can be expressed as:G(s)=1/(s2M+sD+K)
FIG. 1 is a block diagram showing a system of impedance control. When a force F is applied from outside, Δx is displaced according to the impedance characteristics {M, D, K}.
As described above, in the impedance control, a position of the object of control and/or a force acting between the object of control and environment is controlled according to an action of the object of control, by respectively adjusting mass characteristic, damping characteristic and rigidity characteristic of the object of control.